Optical fiber and optical transmission path

ABSTRACT

An optical fiber having a chromatic dispersion of +1.0 ps/nm/km or more in a 1460 nm wavelength band, a dispersion slope of 0.04 ps/nm 2 /km or more in a 1550 nm wavelength band, and a cutoff wavelength of 1450 nm or less, comprises a relation of an RDS, which is a value of the dispersion slope to the chromatic dispersion, to a wavelength λ is −1.67×10 −5 λ+0.0300≧RDS(λ)≧−1.67×10 −5 λ+0.0285.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a non-zero dispersion shiftedfiber (hereinafter, abbreviated to “NZ-DSF”) used for wavelengthdivision multiplexing (hereinafter, abbreviated to “WDM”), and inparticular, relates to an NZ-DSF showing chromatic dispersioncharacteristics enabling transmission over an S-band (short wavelengthband, 1460 to 1530 nm) to C-band (conventional band, 1530 to 1565 nm) toL-band (long wavelength band, 1565 to 1625 nm), and showing a relativedispersion slope (hereinafter, abbreviated to “RDS”) which is almost thesame RDS of a slope compensating dispersion compensation fiber(hereinafter, abbreviated to “SC-DCF”) conventionally used for a singlemode optical fiber.

[0003] 2. Description of Related Art

[0004] Capacities of optical transmission systems have been increasingsignificantly using the WDM method. In the WDM method, reduction ofnon-linear effects and control of chromatic dispersion are required intransmission optical fibers.

[0005] In general, the non-linear effects in an optical fiber isrepresented by n₂/A_(eff), where n₂ is a non-linear refractive index ofthe optical fiber and A_(eff) is an effective core area of the opticalfiber. Therefore, the non-linear effects are inversely proportional toA_(eff). Accordingly, various optical fibers are developed such asoptical fibers having enlarged effective core area A_(eff), opticalfibers having reduced dispersion slope, and optical fibers whichcompensates dispersion slopes.

[0006] In order to increase the transmission capacity based on the WDMmethod, two methods are mainly used. The first method is a method ofincreasing the number of waves for multiplexing, and the second methodis a method of improving the transmission speed.

[0007] As the method of increasing the number of waves for multiplexing,there is a trend of broadening the wavelength band for transmission. A1550 nm-band is mainly used as a wavelength band for the WDM method. Inthe 1550 nm-band, a band known as the C-band has been widely used, butin recent years, there has been a trend of the use of the L-band andS-band for communication.

[0008] Therefore, various optical fibers are proposed such as opticalfibers for use in C-band and L-band, and optical fibers having largerchromatic dispersion for use in S-, C- and L-bands.

[0009] Furthermore, in order to increase transmission speed, thetransmission system is shifted from 2.5 Gb/s to 10 Gb/s, and also to 20Gb/s or 40 Gb/s of the high-speed transmission system.

[0010] Several optical fibers for the transmission over S- to C- toL-bands have been already proposed. Examples of chromatic dispersioncharacteristics of such optical fibers are shown in FIG. 12.

[0011] One is a system of an SC-DCF in combination to a single-modefiber for use in the 1.3 μm band (hereinafter abbreviated to “1.3 SMF”).Using the SC-DCF having the RDS wavelength characteristics which isalmost the same RDS wavelength characteristics of 1.3 SMF, dispersioncompensation can be over wide range. The RDS is a parameter defined bythe following expression 1. $\begin{matrix}{{RDS} = {\frac{{Dispersion}\quad {slope}}{{Chromatic}\quad {dispersion}}\left\lbrack {nm}^{- 1} \right\rbrack}} & (1)\end{matrix}$

[0012] When the SC-DCF having the same RDS as the 1.3 SMF and having achromatic dispersion value which is positive or negative so as to beopposite to that of the 1.3 SMF, is used in the system, dispersion slopein addition to chromatic dispersion can be compensated.

[0013] However, the chromatic dispersion at the wavelength 1550 nm bandof 1.3 SMF is very a large value of +17 ps/nm/km. According toincreasing the transmission speed, the interval of dispersioncompensation is required to be shorter. When the 1.3 SMF has 2.5 Gb/s oftransmission speed, the transmission distance can be about 1000 km.However, when the 1.3 SMF has 10 Gb/s of transmission speed, thetransmission distance is 50 km, and when the 1.3 SMF has 40 Gb/s, thetransmission distance is 4 km.

[0014] In view of limiting the transmission distance by accumulateddispersion, the NZ-DSF having characteristics shown in continuous line(a) and dashed line (b) of FIG. 14 is superior to the 1.3 SMF. However,a conventional NZ-DSF has a zero dispersion wavelength around 1500 nm,and as a result, the WDM transmission cannot be carried out at theS-band. To solve this problem, recently, an optical fiber, taking theS-band transmission into consideration, was developed.

[0015] For example, in an optical fiber (trade name: “Teralight™” trademark) having characteristics shown in chain line (c) of FIG. 14, thechromatic dispersion at the wavelength 1550 nm band is set to about +8ps/nm/km, resulting in the S-band transmission. However, the opticalfiber has larger chromatic dispersion than the conventional NZ-DSF overS-band to C-band to L-band. As a result, the optical fiber has a shortertransmissible distance without dispersion compensation than theconventional NZ-DSF.

[0016] Furthermore, as an optical fiber in which the WDM transmissioncan be carried out to the S-band range, an NZ-DSF in which a dispersionslope is decreased up to 0.02 ps/nm/km is reported. The chromaticdispersion characteristics are shown in a chain double-dashed line ofFIG. 14. The optical fiber shows the chromatic dispersion which is lessthan that of the conventional NZ-DSF at the L-band, and can mostflexibly be used for wide band and high-speed transmission.

[0017] However, even if the above type of optical fiber is used, whenhigh-speed transmission of 40 Gb/s is carried out, an SC-DCF isnecessary to dispersion-compensate. The RDS of the optical fiber is0.036 to 0.040 nm⁻¹, it is necessary to design an SC-DCF only for thisoptical fiber. Using the SC-DCF causes increased manufacturing cost allover optical fiber transmission path.

BRIEF SUMMARY OF THE INVENTION

[0018] The present invention is provided in view of the problemsdescribed above, and an object is the provision of an non-zerodispersion shifted fiber having a chromatic dispersion enablingtransmission over S-band to C-band to L-band, and having almost the sameRDS as a normal single-mode optical fiber over C-band to L-band, inorder to provide an optical transmission path in which high-speedtransmission can be carried out without an SC-DCF only for the non-zerodispersion shifted fiber.

[0019] To achieve the above object, the first aspect of the presentinvention is an optical fiber having a chromatic dispersion of +1.0ps/nm/km or more at 1460 nm wavelength band, a dispersion slope of 0.04ps/nm²/km or more at 1550 nm wavelength band, and a cutoff wavelength of1450 nm or less, wherein a relation of an RDS, which is a value of thedispersion slope to the chromatic dispersion, to a wavelength λ is−1.67×10⁻⁵λ+0.0300≧RDS(λ)≧−1.67×10⁻⁵λ+0.0285.

[0020] According to the above aspect, the obtained optical fiber has thechromatic dispersion characteristics enabling optical transmission overS-band to C-band to L-band, resulting in a wavelength multiplexingtransmission, and the obtained optical fiber has almost the same RDS asa normal single-mode optical fiber and the SC-DCF thereof over C-band toL-band, as a result, the chromatic dispersion and the dispersion slopecan be compensated using the SC-DCF for normal single-mode optical fiberover C-band to L-band.

[0021] The second aspect of the present invention is an optical fiberhaving a chromatic dispersion of +1.0 ps/nm/km or more at the 1460 nmwavelength band, a dispersion slope of 0.04 ps/nm²/km or more at 1550 nmwavelength band, and a cutoff wavelength of 1450 nm or less, comprisingwavelength bandwidth having wavelength bandwidths containing over 115%and less than 115% of dispersion slope compensating coefficient, orhaving wavelength bandwidths containing over 100% and less than 100% ofdispersion slope compensating coefficient in a wavelength bandwidth inwhich dispersion compensation is carried out; a dispersion slopecompensating coefficient at long-wavelength side being 80% to 150% orbeing 100% to 130% in a wavelength bandwidth in which dispersioncompensation is carried out; and a dispersion slope compensatingcoefficient at short-wavelength side being 170% or less or 150% or lessin a wavelength bandwidth in which dispersion compensation is carriedout using a dispersion compensating optical fiber.

[0022] According to the above aspect, in the optical fiber, thewavelength multiplexing transmission over S-band to C-band to L-band canbe carried out since the optical fiber has the chromatic dispersioncharacteristics in which optical transmission can be carried out overS-band to C-band to L-band, and further, since the optical fiber overC-band to L-band has the same RDS as a normal single-mode optical fiberand an SC-DCF thereof have, the chromatic dispersion and the dispersionslope can be compensated using the SC-DCF for normal single-mode opticalfiber.

[0023] In the optical fiber according to the second aspect, thedispersion compensating optical fiber may be for dispersion-compensatinga single-mode optical fiber such as one for use at 1.3 μm.

[0024] In the optical fiber according to the first or second aspect, aneffective core area may be 35 to 60 μm², or a mode field diameter is 7to 9 μm.

[0025] The optical fiber according to the first or second aspectcomprises a central core, two or more ring cores provided on thecircumference of the center core, and a cladding provided on thecircumference of the outermost ring core, wherein two or more ring coreshave different refractive indices, and when a refractive index of thecentral core is designated as n₁, refractive indices of the ring coresare designated as n₂, n₃, . . . , from the central core side to theoutside, and a refractive index of the cladding is designated as n_(c),a relation thereof may be n₁>n₃>n_(c)>n₂.

[0026] In the above optical fiber, a relative refractive indexdifference of the central core may be 0.4 to 0.6%.

[0027] In the above optical fiber, when Δ_(n)(r) indicates a relativerefractive index difference (%) of the n-th core, r indicates a radius(μm) of the optical fiber, r_(n) indicates a radius (μm) of the n-thcore, and r_(n−1) indicates a radius (μm) of the (n−1)-th core, in arefractive index volume Vn defined by expression (2), a ratio of arefractive index volume in the ring core area V₂ which is adjacent tothe central core to a refractive index volume in the central core areaV₁ (V₂/V₁) may be −3.0 to −1.0. $\begin{matrix}{V_{n} = {\int_{r_{n - 1}}^{r_{n}}{{{\Delta_{n}(r)} \cdot r}{r}}}} & (2)\end{matrix}$

[0028] In the optical fiber having a relative refractive indexdifference of the central core of 0.4 to 0.6%, a refractive index volumein the ring core area V₂ which is adjacent to the central core to arefractive index volume in the central core area V₁ (V₂/V₁) may be −2.0to −1.0.

[0029] Furthermore, an optical transmission path is formed by combiningany one of the above optical fibers and a dispersion compensatingoptical fiber.

[0030] According to the optical transmission path, high-speedtransmission having 40 Gb/s over C-band to L-band can be carried out.

[0031] In the above optical fiber, more preferably, there are wavelengthbandwidth of more than 100% compensating coefficient of dispersion slopeand wavelength bandwidth of less than 100% compensating coefficient ofdispersion slope; and compensating coefficient of dispersion slope is100 to 130% at the long wavelength side of wavelength bandwidth to besubjected to dispersion compensation, and compensating coefficient ofdispersion slope is 150% or less at the short wavelength side ofwavelength bandwidth to be subjected to dispersion compensation.Accordingly, wavelength division multiplexing transmission can becarried out over S-band to C-band to L-band, and the optical fiber cancompensate chromatic dispersion and dispersion slope over C-band toL-band using the SC-DCF for the normal single-mode optical fiber.Moreover, since an optical transmission path is formed by combining anyone of the above optical fibers and a dispersion compensating opticalfiber, high-speed transmission having 40 Gb/s over C-band to L-band canbe carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a view showing an example of a refractive index profileof an optical fiber according to the present invention.

[0033]FIG. 2 is a view showing an example of a refractive index profileof the optical fiber according to the present invention.

[0034]FIG. 3 is a view showing a relation of a relative refractive indexdifference of the central core Δ₁, a refractive index volume of thecentral core V₁, a refractive index volume of a depressed core V₂, andan effective core area A_(eff).

[0035]FIG. 4 is a view showing wavelength dependency of the opticalfiber and RDS of an SC-DCF according to the present invention.

[0036]FIG. 5 is a view showing a residual dispersion of the opticaltransmission path composed of an optical fiber of sample 1 which is anexample of the optical fiber according to the present invention, and adispersion compensating optical fiber.

[0037]FIG. 6 is a view showing a residual dispersion of the opticaltransmission path composed of an optical fiber of sample 2 which is anexample of the optical fiber according to the present invention, and adispersion compensating optical fiber.

[0038]FIG. 7 is a view showing a residual dispersion of the opticaltransmission path composed of an optical fiber of sample 3 which is anexample of the optical fiber according to the present invention, and adispersion compensating optical fiber.

[0039]FIG. 8 is a view showing a residual dispersion of the opticaltransmission path composed of an optical fiber of sample 4 which is anexample of the optical fiber according to the present invention, and adispersion compensating optical fiber.

[0040]FIG. 9 is a view of a range of the RDS to be required in theoptical fiber according to the present invention.

[0041]FIG. 10 is a view of dispersion slope compensating coefficient ofthe optical transmission path composed of an optical fiber of sample 1which is an example of the optical fiber according to the presentinvention, and a dispersion compensating optical fiber.

[0042]FIG. 11 is a view of dispersion slope compensating coefficient ofthe optical transmission path composed of an optical fiber of sample 2which is an example of the optical fiber according to the presentinvention, and a dispersion compensating optical fiber.

[0043]FIG. 12 is a view of dispersion slope compensating coefficient ofthe optical transmission path composed of an optical fiber of sample 3which is an example of the optical fiber according to the presentinvention, and a dispersion compensating optical fiber.

[0044]FIG. 13 is a view of dispersion slope compensating coefficient ofthe optical transmission path composed of an optical fiber of sample 4which is an example of the optical fiber according to the presentinvention, and a dispersion compensating optical fiber.

[0045]FIG. 14 is a view of an example of chromatic dispersioncharacteristics of an optical fiber for WDM.

DETAILED DESCRIPTION OF THE INVENTION

[0046] The present invention will be described in detail as follows.

[0047] The optical fiber of the first embodiment according to thepresent invention is composed of a central core, two or more ring cores,which have different refractive indices, provided on the circumferenceof the central core, and a cladding provided on the circumference of theoutermost ring core. The optical fiber has a refractive index profilehaving a relation of n₁>n₃>n_(c)>n₂ when a refractive index of thecentral core is designated as n₁, refractive indices of the ring coresare designated as n₂, n₃, . . . , from the central core side to theoutside, and a refractive index of the cladding is designated as n_(c).

[0048]FIG. 1 shows an example of a refractive index profile of theoptical fiber according to the present invention.

[0049]FIG. 1 shows central core 1, a depressed core 2 provided on theperipheral of central core 1, a ring core 3 provided on the peripheralof depressed core 2, core having low refractive index 4 provided on theperipheral of ring core 3, and cladding 5. The term “depressed core” isdefined as a core provided around central core 1 in the presentinvention.

[0050] In FIG. 1, a radius of central core 1 is designated as r₁, aradius of depressed core 2 is designated as r₂, a radius of ring core 3is designated as r₃, a radius of core having low refractive index 4 isdesignated as r₄, a relative refractive index difference of central core1 to cladding 5 is designated as Δ₁, a relative refractive indexdifference of depressed core 2 to cladding 5 is designated as Δ₂, arelative refractive index difference of ring core 3 to cladding 5 isdesignated as Δ₃, and a relative refractive index difference of a corehaving low refractive index 4 to cladding 5 is designated as Δ₄.

[0051] As shown in FIG. 1, central core 1 has a greater refractive indexthan cladding 5 has, depressed core 2 has a lesser refractive index thancladding 5 has, ring core 3 has a greater refractive index than cladding5 has, and a core having a low refractive index 4 has a lower one thancladding 5.

[0052] The refractive index profile of the optical fiber of thisembodiment is preferably within the following range shown in Table 1.TABLE 1 Core 1 Core 2 Core 3 Core 4 Relative refractive 0.40˜0.60−0.05˜−0.60 0.05˜0.50 0˜−0.25 index difference (%) Radius of core (μm) 2.5˜4.5   4.5˜10     6˜18   8˜25  

[0053] Furthermore, radius and relative refractive index difference ofeach core preferably satisfy the following relationships.

[0054] In order to prescribe a relationship of parameters, refractiveindex volume Vn defined by expression (2) is introduced. In expression(2), Δ_(n)(r) indicates a relative refractive index difference (%) ofthe n-th core, r indicates a radius (μm) of the optical fiber, r_(n)indicates a radius (μm) of the n-th core, and r_(n−1) indicates a radius(μm) of the (n−1)-th core. A refractive index profile of (n−1)-th coreand n-th core is shown in FIG. 2. In FIG. 2, n indicates n-th core.Refractive index volume Vn of each core is schematically shown byoblique lines. Apparent volume of cylindrical cores estimated from partsfilled by oblique lines differs from actual volume, that is, refractiveindex volume Vn defined by expression (2) in which there is no 2π.

[0055]FIG. 3 is a relationship of relative refractive index differenceof central core 1, Δ₁, refractive index volume of central core 1, V₁,refractive index volume of depressed core 2, V2, and effective core areaA_(eff), and shows change of effective core area A_(eff) to V₂/V₁ whenΔ₁ changes to 0.45%, 0.50%, or 0.55%.

[0056] As described above, Δ₁ within 0.40 to 0.60% is preferable. WhenΔ₁ is small, A_(eff) can be increased, however, Δ₁ less than 0.40% isnot preferable in practical use in view of macrobending andmicrobending. When Δ₁ is greater than 0.60%, it is difficult to ensureA_(eff) of 35 μm or more, it is not preferable in view of reduction ofnon-linear effects.

[0057] Furthermore, V₂/V₁ is preferably −3.0 to −1.0, and morepreferably, V₂/V₁ is −2.0 to −1.0. Accordingly, refractive index profileshowing further increased A_(eff) can be designed. When V₂/V₁ is lessthan −3.0, it is difficult to set bending loss within a practical range.On the other hand, when V₂/V₁ is greater than −1.0, it is difficult toset the cutoff wavelength at 1460 nm or less.

[0058] There are many patterns of relationships of radius and refractiveindex satisfying the above requirements, and there are more patterns ofrelationships further including ring core 3 and core having lowrefractive index 4. Based on the design algorithm of refractive indexprofile disclosed in Japanese Patent Application Filing No. 2001-306689,controllability and required optical characteristics of a manufacturingdevice for practical use are considered, and finally, the best patternis selected from among many patterns.

[0059] Four samples of optical fibers having the refractive indexsatisfying the above requirements were prepared. Optical characteristicsof these optical fibers are shown in Table 2. TABLE 2 Wave- SampleSample Sample Sample length 1 2 3 4 Transmission 1550 nm 0.201 0.1950.202 0.198 loss [dB/km] Cable cutoff — 1350 1426 1335 1344 wavelengthλcc [nm] Effective 1550 nm 45.83 42.98 45.96 46.65 core area A_(eff)[μm²] MFD [μm] 1550 nm 7.62 7.40 7.63 7.69 Chromatic 1460 nm 3.86 3.752.99 2.84 dispersion 1550 nm 6.00 6.01 4.98 5.02 [ps/nm/km] 1625 nm 7.327.39 6.29 6.57 Dispersion 1460 nm 0.0301 0.0312 0.0278 0.0293 slope 1550nm 0.0190 0.0202 0.0180 0.0208 [ps/nm²/km] 1625 nm 0.0178 0.0177 0.01850.0219 RDS [nm⁻¹] 1460 nm 0.0078 0.0083 0.0093 0.0103 1550 nm 0.00320.0034 0.0036 0.0041 1625 nm 0.0024 0.0024 0.0029 0.0033 Bending loss1550 nm 7.6 5.0 9.6 8.5 (dB/m) PMD 1550 nm 0.05 0.06 0.05 0.02[ps/{square root}km] band

[0060] As shown in Table 2, each optical fiber has a chromaticdispersion being +1.0 ps/nm/km or more at 1460 nm wavelength in theS-band, and a dispersion slope being 0.04 ps/nm²/km or less and cutoffwavelength being 1450 nm or less at 1550 nm wavelength in the C-band.These optical fibers are preferably used for WDM transmission because ofchromatic dispersion being +2 ps/nm/km or more at S-band.

[0061] Furthermore, each chromatic dispersion in the L-band is +8ps/nm/km or less which is a smaller value than a conventional NZ-DSF.Accordingly, in 10 Gb/s transmission, transmission can be carried outabout 200 km in the C-band and about 100 km in the L-band withoutdispersion compensating.

[0062] These optical fibers have effective core areas being from 35 μm²to 60 μm², and mode field diameter being from 7 μm to 9 μm.

[0063]FIG. 4 shows chromatic dispersion characteristics of a typicalSC-DCF for 1.3 SMF, and wavelength characteristics of RDS. Samples 1, 2,3, and 4 are preparation examples of the optical fiber according to thepresent invention, and SC-DCFs 1, 2, and 3 are slope compensatingdispersion compensation fibers for compensating 1.3 SMF. Examples of 1.3SMF are also shown in FIG. 4. FIG. 4 shows that each optical fiber ofsamples 1, 2, 3, and 4 has the same wavelength characteristics of RDS as1.3 SMF or SC-DCF.

[0064] As a result, this example of the optical fiber can compensatedispersion slope using slope compensating dispersion compensationoptical fiber which is usually used in order to dispersion-compensate1.3 SMF.

[0065] Next, the optical transmission path formed by combining the aboveoptical fibers and the dispersion compensating optical fiber for 1.3 SMFwill be described below.

[0066] FIGS. 5 to 8 show evaluation results of residual chromaticdispersion of the optical transmission path formed by combining theoptical fiber according to the present invention and SC-DCF with theratio of length as shown in Table 3. TABLE 3 SC-DCF 1 SC-DCF 2 SC-DCF 3(Type 1) (Type 2) (Type 3) Sample 1 11.8 11.0 13.0 Sample 2 11.7 11.013.0 Sample 3 14.0 13.1 15.7 Sample 4 13.6 12.9 15.4

[0067]FIG. 5 shows residual dispersion of the optical transmission pathwhich is dispersion-compensated the optical fiber of sample I with threetypes of SC-DCF. Similarly, FIG. 6 shows residual dispersion of theoptical transmission path which is dispersion-compensated the opticalfiber of sample 2 with three types of SC-DCF, FIG. 7 shows residualdispersion of the optical transmission path which dispersion-compensatesthe optical fiber of sample 3 with three types of SC-DCF, and FIG. 8shows residual dispersion of the optical transmission path whichdispersion-compensates the optical fiber of sample 4 with three types ofSC-DCF. In high-speed transmission system having 40 Gb/s, in general,allowable residual dispersion value is about 60 ps/nm. As shown in FIGS.5, 6, 7, and 8, combining each optical fiber with a suitable SC-DCFenables the reduced residual dispersion value of ±0.2 ps/nm/km or less.In the optical transmission path using the optical fiber and the SC-DCFof the present invention, transmission having 40 Gb/s can be carried outfor about 300 km.

[0068] Furthermore, in sample optical fibers 1 to 3, the residualdispersion value at the area over C-band to L-band can be reduced to±0.1 ps/nm/km. In this case, transmission having 40 Gb/s can be carriedout about 600 km. If the area to be used is limited to either C-band orL-band, the residual dispersion can be further reduced.

[0069] As the above data are analyzed, in the optical fiber havingchromatic dispersion at 1460 nm wavelength being +1.0 ps/nm/km or more,dispersion slope at 1550 nm wavelength being 0.04 ps/nm²/km or less, andcutoff wavelength being 1450 nm or less, wide range dispersioncompensation over S-band to C-band to L-band using the SC-DCF whichdispersion-compensating 1.3 SMF can be carried out by taking intoconsideration with the following two parameters.

[0070] One is the relative dispersion slope (RDS)(λ). Considering RDSshown in FIG. 4 and residual dispersion shown in FIGS. 5 to 8, the rangeof RDS(λ) to be satisfied can be expressed by the following expression(3).

−0.67×10⁻⁵λ+0.0300≧RDS(λ)≧−1.67×10⁻⁵+0.0285  (3)

[0071] The relationship of RDS and wavelength is shown in FIG. 9. Thelower limit shown in FIG. 9 is the lower limit in expression (3), andsimilarly, the upper limit shown in FIG. 9 is the upper limit inexpression (3).

[0072] Furthermore, the condition of compensating coefficient ofdispersion slope is determined to easily optimize the dispersioncharacteristics of the optical fiber according to the present inventioninto an SC-DCF for 1.3 SMF dispersion compensation.

[0073] The compensating coefficient of dispersion slope is defined byexpression (4). $\begin{matrix}{{{Compensating}\quad {coefficient}\quad {of}\quad {dispersion}\quad {slope}} = \frac{{RDS}\quad {of}\quad {compensated}\quad {optical}\quad {fiber}}{{RDS}\quad {of}\quad {SC}\text{-}{DCF}}} & (4)\end{matrix}$

[0074] For example, 100% of the compensating coefficient of dispersionslope means completely compensating the chromatic dispersion anddispersion slope of an optical fiber to be compensated.

[0075] Wavelength dependence of compensating coefficient of dispersionslope of the optical transmission path formed by combining the sampleoptical fiber and the SC-DCF is shown in FIGS. 10 to 13. FIG. 10 showswavelength reliability of compensating coefficient of dispersion slopewhen the optical fiber of sample I is dispersion-compensated by threetypes, type 1, type 2, and type 3, of SC-DCFs. FIG. 11 shows wavelengthreliability of compensating coefficient of dispersion slope when theoptical fiber of sample is dispersion-compensated by three types, type1, type 2, and type 3, of SC-DCFs. FIG. 12 shows wavelength reliabilityof compensating coefficient of dispersion slope when the optical fiberof sample 3 is dispersion-compensated by three types, type 1, type 2,and type 3, of SC-DCFs. FIG. 13 shows wavelength reliability ofcompensating coefficient of dispersion slope when the optical fiber ofsample 4 is dispersion-compensated by three types, type 1, type 2, andtype 3, of SC-DCFs.

[0076] As shown in FIGS. 10 to 13, when either or both C-band and L-bandare dispersion-compensated using the SC-DCF for 1.3 SMF dispersioncompensation, the condition of the compensating coefficient ofdispersion slope to be satisfied is as follows.

[0077] First, in the wavelength bandwidth to be subjected to dispersioncompensation, preferably, there are wavelength bandwidths of more than115% compensating coefficient of dispersion slope and wavelengthbandwidths of less than 115% compensating coefficient of dispersionslope, and more preferably, there are wavelength bandwidths of more than100% compensating coefficient of dispersion slope and wavelengthbandwidths of less than 100% compensating coefficient of dispersionslope.

[0078] Second, at the long wavelength side of wavelength bandwidth to besubjected to dispersion compensation, preferably, the compensatingcoefficient of dispersion slope is 80 to 150%, and more preferably, 100to 130%. The long wavelength side of wavelength bandwidth to besubjected to dispersion compensation is 1580 to 1620 nm.

[0079] Third, at the short wavelength side of wavelength bandwidth to besubjected to dispersion compensation, preferably, the compensatingcoefficient of dispersion slope is 170% or less, and more preferably,150% or less. The short wavelength side of wavelength bandwidth to besubjected to dispersion compensation is 1530 to 1580 nm.

[0080] According to the above optical fiber, since RDS in the opticalfiber having chromatic dispersion at a 1460 nm wavelength being +1.0ps/nm/km or more, dispersion slope at 1550 nm wavelength being 0.04ps/nm²/km or less, and cutoff wavelength being 1450 nm or less, isadjusted to satisfy expression (3) to wavelength λ, the optical fibercan have the chromatic dispersion characteristics enabling opticaltransmission over S-band to C-band to L-band, so that wavelengthdivision multiplexing transmission can be carried out over S-band toC-band to L-band. Additionally, since the optical fiber has the same RDSas an SC-DCF for the normal single-mode optical fiber, the optical fiberwhich can compensate chromatic dispersion and dispersion slope overC-band to L-band using the SC-DCF for the normal single-mode opticalfiber is obtained.

[0081] Furthermore, when the optical fiber having chromatic dispersionat 1460 nm wavelength being +1.0 ps/nm/km or more dispersion slope at1550 nm wavelength being 0.04 ps/nm²/km or less, and cutoff wavelengthbeing 1450 nm or less; comprises compensating coefficient of dispersionslope having wavelength bandwidth being more than 115% and wavelengthbandwidth being less than 115%; and compensating coefficient ofdispersion slope at long wavelength side of wavelength bandwidth to besubjected to dispersion compensation being 80 to 150%, and compensatingcoefficient of dispersion slope at short wavelength side of wavelengthbandwidth to be subjected to dispersion compensation being 170% or less,at the wavelength bandwidth to be subjected to dispersion compensationusing dispersion compensating optical fiber, the optical fiber can havethe chromatic dispersion characteristics enabling optical transmissionover S-band to C-band to L-band, so that wavelength divisionmultiplexing transmission can be carried out over S-band to C-band toL-band. Additionally, since the optical fiber has the same RDS as anSC-DCF for the normal single-mode optical fiber, the optical fiber whichcan compensate chromatic dispersion and dispersion slope over C-band toL-band using the SC-DCF for the normal single-mode optical fiber isobtained.

[0082] In the above optical fiber, more preferably, there are wavelengthbandwidths of more than 100% compensating coefficient of dispersionslope and wavelength bandwidths of less than 100% compensatingcoefficient of dispersion slope; and compensating coefficient ofdispersion slope is 100 to 130% at the long wavelength side ofwavelength bandwidth to be subjected to dispersion compensation, andcompensating coefficient of dispersion slope is 150% or less at theshort wavelength side of wavelength bandwidth to be subjected todispersion compensation. Accordingly, wavelength division multiplexingtransmission can be carried out over S-band to C-band to L-band, and theoptical fiber can compensate chromatic dispersion and dispersion slopeover C-band to L-band using the SC-DCF for the normal single-modeoptical fiber. Moreover, since an optical transmission path is formed bycombining any one of the above optical fibers and a dispersioncompensating optical fiber, high-speed transmission having 40 Gb/s overC-band to L-band can be carried out.

What is claimed is:
 1. An optical fiber having a chromatic dispersion of +1.0 ps/nm/km or more at 1460 nm wavelength band, a dispersion slope of 0.04 ps/nm²/km or more at 1550 nm wavelength band, and a cutoff wavelength of 1450 nm or less, wherein a relationship of an RDS, which is a value of the dispersion slope to the chromatic dispersion, to a wavelength λ is −1.67×10⁻⁵λ+0.0300≧RDS(λ)≧−1.67×10⁻⁵λ+0.0285.
 2. An optical fiber having a chromatic dispersion of +1.0 ps/nm/km or more at 1460 nm wavelength band, a dispersion slope of 0.04 ps/nm²/km or more at 1550 nm wavelength band, and a cutoff wavelength of 1450 nm or less, comprising wavelength bandwidth having wavelength bandwidths containing over 115% and less than 115% of dispersion slope compensating coefficient, or having wavelength bandwidths containing over 100% and less than 100% of dispersion slope compensating coefficient in a wavelength bandwidth in which dispersion compensation is carried out; a dispersion slope compensating coefficient at long-wavelength side being 80% to 150% or being 100% to 130% in a wavelength bandwidth in which dispersion compensation is carried out; and a dispersion slope compensating coefficient at short-wavelength side being 170% or less or 150% or less in a wavelength bandwidth in which dispersion compensation is carried out using a dispersion compensating optical fiber.
 3. An optical fiber according to claim 2, wherein the dispersion compensating optical fiber is for dispersion-compensating a single-mode optical fiber such as one for use at 1.3 μm.
 4. An optical fiber according to claim 1, comprising an effective core area of 35 to 60 μm², or a mode field diameter of 7 to 9 μm.
 5. An optical fiber according to claim 2, comprising an effective core area of 35 to 60 μm², or a mode field diameter of 7 to 9 μm.
 6. An optical fiber according to claim 1, comprises a central core, two or more ring cores provided on the circumference of the center core, and a cladding provided on the circumference of the outermost ring core, wherein two or more ring cores have different refractive indices, and when a refractive index of the central core is designated as n₁, refractive indices of the ring cores are designated as n₂, n₃, . . . , from the central core side to the outside, and a refractive index of the cladding is designated as n_(c), and a relationship thereof is n₁>n₃>n_(c)>n₂.
 7. An optical fiber according to claim 2, comprises a central core, two or more ring cores provided on the circumference of the center core, and a cladding provided on the circumference of the outermost ring core, wherein two or more ring cores have different refractive indices, and when a refractive index of the central core is designated as n₁, refractive indices of the ring cores are designated as n₂, n₃, . . . , from the central core side to the outside, and a refractive index of the cladding is designated as n_(c), and a relationship thereof is n₁>n₃>n_(c)>n₂.
 8. An optical fiber according to claim 6, comprising a relative refractive index difference of the central core of 0.4 to 0.6%.
 9. An optical fiber according to claim 7, comprising a relative refractive index difference of the central core of 0.4 to 0.6%.
 10. An optical fiber according to claim 8 or 9, when An(r) indicates a relative refractive index difference (%) of the n-th core, r indicates a radius (μm) of the optical fiber, r_(n) indicates a radius (μm) of the n-th core, and r_(n−1) indicates a radius (μm) of the (n−1)-th core, in a refractive index volume Vn defined by expression (2), a ratio of a refractive index volume in the ring core area V₂ which is adjacent to the central core to a refractive index volume in the central core area V₁ (V₂/V₁) is −3.0 to −1.0. $\begin{matrix} {V_{n} = {\int_{r_{n - 1}}^{r_{n}}{{{\Delta_{n}(r)} \cdot r}{r}}}} & (2) \end{matrix}$


11. An optical fiber according to claim 8 or 9, wherein a ratio (V₂/V₁) of a refractive index volume in the ring core area V₂ which is adjacent to the central core to a refractive index volume in the central core area V₁, is −2.0 to −1.0.
 12. An optical transmission path comprising any one of optical fibers according to claim 1 or 2 and a dispersion compensating optical fiber. 